Retro-reflectors are installed or attached to various types of traffic safety facilities such as various types of traffic signs, pavement markers, delineators, and traffic tripods, or items such as safety clothing, automobiles, bicycles, hats, and shoes, of which the visibility needs to be ensured at night, and the retro-reflectors may improve visibility of these items by retro-reflecting incident light, which enters from a front side, toward a light source that emits the light.
As the retro-reflectors applied to these items in the related art, retro-reflectors provided with glass beads or cube corners have been often used. Since the retro-reflectors in the related art have different retro-reflection characteristics varying depending on incident angles of incident light, the retro-reflectors have advantages and disadvantages.
For example, retro-reflection efficiency of the retro-reflector using the glass beads is uniform regardless of incident angles, but the retro-reflector using the glass beads has problems in that retro-reflection efficiency is low overall, and a reflection function deteriorates in a case in which water is attached to the surface of the retro-reflector.
Further, the retro-reflector using the cube corners in the related art has high retro-reflectivity for light having a small incident angle, that is, front light, but rapidly degrades brightness for lateral light having a large incident angle, such that a range of incident angles within which retro-reflection is enabled, that is, retro-reflection visibility is very narrow. Moreover, it is very difficult to design and change a direction of retro-reflection visibility in order to mainly retro-reflect light having a large incident angle.
To solve the problems, the present applicant has developed ‘Retro-Reflection Unit and Retro-Reflector (Korean Patent Application No. 10-2006-7038)’ which have a complex total-reflection prismatic retro-reflective structure in which reflective surfaces, which are orthogonal to each other, are arranged, in a steplike manner, on a reflective surface of two reflective surfaces which are orthogonal to each other, such that overall retro-reflectivity is high, and particularly, a direction of a main reflection orientation, which is defined as an incident direction in which retro-reflectivity is highest, may be very easily changed without limitation on an angle with respect to a normal direction of an incident plane during a design process.
However, the retro-reflection unit of the retro-reflector includes two reflective surfaces (a shared reflective surface and a step portion), such that there is a problem in that retro-reflection is enabled only for incident light within a particular incident angle range, and thus a retro-reflection range is very narrow. For example, in a case in which the retro-reflector is developed for front light, very high retro-reflection efficiency is implemented for incident light having an incident angle of zero (0) degree, but in a case in which an incident angle becomes 10 degrees or more, the incident light penetrates the shared reflective surface such that a retro-reflection function of some retro-reflection units is degraded, and as a result, there is a problem in that retro-reflection performance is low for lateral light, and in a case in which the retro-reflector is developed for lateral light, there is a problem in that retro-reflection efficiency is very low for front light with compared to lateral light. Accordingly, since the retro-reflector of Korean Patent Application No. 10-2006-7038 has a very narrow reflection range, there is a problem in that applicability to front light or lateral light is restricted.